The present invention relates generally to flight control actuators and more specifically, to fin actuators that substantially limit backlash in portable missiles while meeting strict construction constraints.
In today""s conflict scenarios the warfighter must be versatile and on the move. More often munitions and weapons are required to be man packable and portable. Funds for warfighting are stretched to their fullest, adding the requirement of lower unit cost. One alternative that meets these requirements includes a man packable, portable, and economical shoulder launched missile. In order to be man portable the missile must be lightweight and compact.
One specific area of concern in the construction of a portable missile is the operation of the fins or wings. Missile control fins are commonly positioned by actuators mounted within the missile body in an actuator section. The actuator exerts appropriate rotational torque and control on the fin in response to commands from the guidance control system to maneuver the missile. In a portable missile, there exists for a fin actuator stringent requirements of size, weight, torque and angle of deflection delivered to the fin shaft, backlash, cost, and ease of construction. The small body diameter requirement intensifies the mechanical problem of converting rotary motion from a motor into torque to be applied to a fin shaft. In addition, all of the missile components must withstand great temperature variations due to their shipment and use in many different climates.
Total backlash refers to the additive xe2x80x9cslopxe2x80x9d or xe2x80x9cplayxe2x80x9d that exists between the mating components in a fin actuator, measured as a total angular value at the fin shaft as the fin or wing rotates about its axis. The various backlash values of the components contribute to the overall total backlash. Friction between components and thermal expansion contribute to total backlash. An excessive amount of backlash in the fins or wings creates a situation in which directional control of the missile is much more complicated for the guidance control system.
Many types of conventional fin actuators were examined to meet the fin actuator requirements. A worm gear drive small enough to meet the demands of the missile would require custom manufacture of the gears, and since there is inadequate room to fully support the worm gear a large amount of friction would result. It would be difficult (costly) to manufacture a worm gear to meet the physical space requirements. A bevel or miter gear actuator must be set, preloaded and shimmed to maintain the proper clearances. Also, gears are subject to expansion and contraction with temperature, contributing to backlash. In a production environment, positioning gears to achieve correct spacing is difficult, contributing to the cost. Custom fabrication and assembly would be required for this type of actuator, thereby exceeding the cost and ease of fabrication requirements. The use of a stepper motor linear actuator was also precluded due to the dimensions of the motor. In addition, these drives do not accommodate significant side loads that can be generated while in flight. Hydraulic type actuators also exceeded the physical space requirements. In general, the final result in the actuators considered was an excessive amount of backlash, along with difficulty meeting size and weight parameters.
Therefore it would be desirable to provide a fin or wing actuator that will meet the specific requirements previously discussed for a low cost, man-portable missile.
The present invention relates to a novel fin actuator for a portable missile and a method of using the same. One aspect of the present invention includes a fin or wing actuator that meets very strict criteria to fit within a compact, portable missile while substantially limiting backlash. Another aspect of the present invention is a method of fin actuation in a portable missile while substantially limiting backlash.
In an embodiment of the present invention a fin actuator(s) in a portable missile that substantially limits backlash includes a means for rotating a power shaft operatively configured to rotate the power shaft in a forward direction and a reverse direction; a means for converting the rotational movement of the power shaft to linear movement, including a lead screw fixedly coupled to the power shaft with a lead nut threadingly engaged and moving linearly along the lead screw in relation to the direction of rotation of the power shaft; and a means for converting the linear movement of the lead nut to rotational movement of a fin shaft, including the lead nut operatively coupled to a crank arm fixedly coupled to the fin shaft, effecting the rotation of the fin shaft according to the linear movement of the lead nut.
Another aspect of the present invention includes a method for fin actuation, in a portable missile, that substantially limits backlash. An example of the method includes but is not limited to, providing a means operatively configured for rotating a power shaft in a forward direction and a reverse direction, providing a means for converting rotational movement of the power shaft to linear movement via a lead screw fixedly coupled to the power shaft and having a lead nut threadingly engaged moving linearly along the lead screw in relation to the direction of rotation of the power shaft, and providing a means for converting the linear movement to rotational movement of a fin shaft, including operatively coupling the lead nut to a crank arm that is fixedly coupled to the fin shaft, effecting the rotation of the fin shaft according to the linear movement of the lead nut.
In an embodiment of the present invention the lead screw, lead nut, and crank arm are so constructed and coupled as to limit the total backlash of the actuator(s), measured at the fin shaft, to less than about 0.1 degrees. In additional embodiments of the present invention the actuator(s) is dimensioned and configured to fit in a portable missile of less than about 5 lbs, of less than about 2 inches in diameter, and/or of less than about 3 inches in length. In additional embodiments of the present invention the actuator(s) is providing at least about 50 oz-in of torque to the fin shaft and/or providing from at least about xe2x88x9220 degrees to at least about +20 degrees of deflection of the fin shaft. In another embodiment of the present invention the actuator(s) includes the crank arm and the fin shaft combined as a unitary structure. It is noteworthy that multiple embodiments of the present invention shall be used to operate multiple fins on a portable missile.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the present invention, as claimed. These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.